This invention relates generally to ignition systems for internal combustion engines, and in particular to a spark timing control device and control method for such ignition systems which is especially advantageous during the starting of the engine and during low speed conditions.
In order to improve the starting of an engine or improve the running of the engine during idling, a choke valve is generally provided to create a rich fuel mixture by reducing the air intake. While an enriched fuel mixture is helpful during starting and idling conditions, it is not completely effective in providing for smooth engine operation, since the spark timing must also be considered as well. If a relatively long time is provided before a sparking potential is reached in the ignition system, it will be appreciated that a significant portion of the enriched fuel mixture may be exhausted without being burnt in the engine cylinders. As a consequence, the engine may have difficulty in starting or running smoothly during a low speed condition such as idling. Additionally, acceleration from these conditions may not be as stable as could be achieved by the engine.
Generally, in prior ignition systems, spark timing has been a mechanical function of the engine speed, such that the spark time is advanced as the engine speed is increased and retarded as the engine speed is decreased. Thus, during low rotational engine speeds, such as starting and idling, the spark timing will be retarded. In other words, a relatively long time is provided before a sparking potential is reached in the ignition system. Additionally, in these prior ignition systems, an engine speed level is usually provided where the spark timing will reach a predetermined lower limit. Accordingly, even if the engine speed decreased below this level, the spark timing will not increase beyond this predetermined limit. However, this lower spark timing limit is generally too long to completely burn an enriched fuel mixture which will result when the choke is used during starting and idling conditions of the engine.
It is therefore a principal object of the presnet invention to provide a spark timing control device for an internal combustion engine ignition system which improves the starting and low speed running conditions of the engine.
It is another object of the present invention to provide a spark timing control device which is capable of advancing the spark timing during starting and low speed running conditions of the engine.
It is a further object of the present invention to provide a spark timing control device which is responsive to temperature during the starting of the engine.
It is an additional object of the present invention to provide a spark timing control in a breakerless magneto-type ignition system which employs a variable time consant to control the time at which the ignition system will produce a sparking potential.